Halani Sameer H, Safain Mina G, Heilman Carl B
Department of Neurosurgery, Tufts Medical Center and Tufts University School of Medicine, Boston, Massachusetts 02111, USA.
J Neurosurg Pediatr. 2013 Jul;12(1):62-6. doi: 10.3171/2013.4.PEDS12609. Epub 2013 May 10.
Arachnoid cysts are common, accounting for approximately 1% of intracranial mass lesions. Most are congenital, clinically silent, and remain static in size. Occasionally, they increase in size and produce symptoms due to mass effect or obstruction. The mechanism of enlargement of arachnoid cysts is controversial. One-way slit valves are often hypothesized as the mechanism for enlargement. The authors present 4 cases of suprasellar prepontine arachnoid cysts in which a slit valve was identified. The patients presented with hydrocephalus due to enlargement of the cyst. The valve was located in the arachnoid wall of the cyst directly over the basilar artery. The authors believe this slit valve was responsible for the net influx of CSF into the cyst and for its enlargement. They also present 1 case of an arachnoid cyst in the middle cranial fossa that had a small circular opening but lacked a slit valve. This cyst did not enlarge but surgery was required because of rupture and the development of a subdural hygroma. One-way slit valves exist and are a possible mechanism of enlargement of suprasellar prepontine arachnoid cysts. The valve was located directly over the basilar artery in each of these cases. Caudad-to-cephalad CSF flow during the cardiac cycle increased the opening of the valve, whereas cephalad-to-caudad CSF flow during the remainder of the cardiac cycle pushed the slit opening against the basilar artery and decreased the size of the opening. Arachnoid cysts that communicate CSF via circular, nonslit valves are probably more likely to remain stable.
蛛网膜囊肿很常见，约占颅内占位性病变的1%。大多数是先天性的，临床上无症状，大小保持不变。偶尔，它们会因占位效应或梗阻而增大并产生症状。蛛网膜囊肿增大的机制存在争议。单向裂隙瓣膜常被认为是增大的机制。作者报告了4例鞍上脑桥前蛛网膜囊肿病例，其中发现了裂隙瓣膜。这些患者因囊肿增大而出现脑积水。瓣膜位于囊肿蛛网膜壁上，正好在基底动脉上方。作者认为这个裂隙瓣膜是脑脊液净流入囊肿并导致其增大的原因。他们还报告了1例中颅窝蛛网膜囊肿病例，该囊肿有一个小圆形开口，但没有裂隙瓣膜。这个囊肿没有增大，但由于破裂和硬膜下积液的形成而需要手术。单向裂隙瓣膜确实存在，是鞍上脑桥前蛛网膜囊肿增大的一种可能机制。在这些病例中，瓣膜都正好位于基底动脉上方。心动周期中脑脊液从尾端向头端流动会增加瓣膜的开口，而心动周期其余时间脑脊液从头端向尾端流动则会将裂隙开口压向基底动脉并减小开口大小。通过圆形非裂隙瓣膜与脑脊液相通的蛛网膜囊肿可能更有可能保持稳定。
